3

Looking at these two transactions for example: tx1 and tx2. tx1 is an OP_RETURN trasaction, tx2 is a normal transaction.

raw hex from tx1 (OP_RETURN): 0100000000010173a9eafb38a83662d28a5c885165c7aa3f27694e39f0ba4e4fc86d98ff3dd2d60000000000ffffffff0200000000000000004b6a494575726f7065206973207469726564206f66206265696e67207375627365727669656e7420746f207468652055532e204c6f6e67206c6976652052757373696120f09f87b7f09f87ba2a940600000000002251203e4c971ecd3ad020833cbd4b2ecdf1f229d430dfa48adc3203f5f79c801dfb9901407ac1f8560a33867cdfa3ad136488ed7f4f5d1f4fc6a32822d8dd6c5e47e9317f0f2a4381349a803d223773711d6df8303e9c23e60782633450c735b2275d9a2100000000

raw hex from tx2: 0200000000010191fd88fc50bd8932c8da649e0c54b42ab3598a89c420c28bf6fad2d443711dbd2e00000000ffffffff016bef0c000000000017a9140afdb9b53981bfac9c53d01f6389b5ebecf8499f8702483045022100f0d0944b835095b5fcad86df999831ae3eade37c0eb68649b83a55ca5f1854af0220231561ec647b7bd9179c5f809e878a4cfd09818514b42ca8a274b11dfaa3a3ed012103e5d3e103615a36046dfbe880d6fb4c47e5227d8176635310c5dd08d5aa43f99c00000000

What am I looking for?

1 Answer 1

5

You can use bitcoin-cli to decode the transaction and get a sense of what is going on:

bitcoin-cli decoderawtransaction 0100000000010173...275d9a2100000000

That returns:

{
  "txid": "00fddd900b735a88ab0ef5eeaa3efbc869d4e52493da8a9467ec782355cb39ff",
  "hash": "b4c4817e908d9ba317e9b1a08180b51c0ce77adca946e7f894560fb07447acf8",
  "version": 1,
  "size": 246,
  "vsize": 195,
  "weight": 780,
  "locktime": 0,
  "vin": [
    {
      "txid": "d6d23dff986dc84f4ebaf0394e69273faac76551885c8ad26236a838fbeaa973",
      "vout": 0,
      "scriptSig": {
        "asm": "",
        "hex": ""
      },
      "txinwitness": [
        "7ac1f8560a33867cdfa3ad136488ed7f4f5d1f4fc6a32822d8dd6c5e47e9317f0f2a4381349a803d223773711d6df8303e9c23e60782633450c735b2275d9a21"
      ],
      "sequence": 4294967295
    }
  ],
  "vout": [
    {
      "value": 0.00000000,
      "n": 0,
      "scriptPubKey": {
        "asm": "OP_RETURN 4575726f7065206973207469726564206f66206265696e67207375627365727669656e7420746f207468652055532e204c6f6e67206c6976652052757373696120f09f87b7f09f87ba",
        "desc": "raw(6a494575726f7065206973207469726564206f66206265696e67207375627365727669656e7420746f207468652055532e204c6f6e67206c6976652052757373696120f09f87b7f09f87ba)#vxme4rep",
        "hex": "6a494575726f7065206973207469726564206f66206265696e67207375627365727669656e7420746f207468652055532e204c6f6e67206c6976652052757373696120f09f87b7f09f87ba",
        "type": "nulldata"
      }
    },
    {
      "value": 0.00431146,
      "n": 1,
      "scriptPubKey": {
        "asm": "1 3e4c971ecd3ad020833cbd4b2ecdf1f229d430dfa48adc3203f5f79c801dfb99",
        "desc": "rawtr(3e4c971ecd3ad020833cbd4b2ecdf1f229d430dfa48adc3203f5f79c801dfb99)#nkpjq33l",
        "hex": "51203e4c971ecd3ad020833cbd4b2ecdf1f229d430dfa48adc3203f5f79c801dfb99",
        "address": "bcrt1p8exfw8kd8tgzpqeuh49jan037g5agvxl5j9dcvsr7hmeeqqalwvs884ffw",
        "type": "witness_v1_taproot"
      }
    }
  ]
}

You can see how, in the output section of the transaction, the first output is an OP_RETURN output, and that the data associated to it is:

4575726f7065206973207469726564206f66206265696e67207375627365727669656e7420746f207468652055532e204c6f6e67206c6976652052757373696120f09f87b7f09f87ba

Also, notice how the OP_RETURN opcode is 0x6a (you can check the bitcoin wiki for that).

Therefore, the piece you're looking for inside the hex transaction is:

6a494575726f7065206973207469726564206f66206265696e67207375627365727669656e7420746f207468652055532e204c6f6e67206c6976652052757373696120f09f87b7f09f87ba

You may also notice there is an additional byte of information between the OP_RETURN opocode and the data: 0x49. That's the size of the associated data in bytes (encoded in hex). 49 hex equals 73 dec, so the length is 73 bytes or 146 hex characters.

1
  • 1
    I'm writing some Rust code and I'll need to parse the raw hex and then decode it, w/o libs. Thanks, this answered my question.
    – luisschwab
    Jan 22, 2023 at 0:02

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge you have read our privacy policy.

Not the answer you're looking for? Browse other questions tagged or ask your own question.